Yes, locking her in the bathroom with a dish of water and a litter box overnight. But what goes in the litter box to encourage her to use it? I’ve heard styrofoam packing peanuts, but that doesn’t make sense to me. Don’t they dissolve and contaminate the sample?
I’d like to keep from having to have the vet get the sample (and so would the vet).
When I had to do this, my vet gave me these tiny plastic beads that I put into an empty litter pan with a clean plastic liner; they were enough like litter for the cat to feel comfortable peeing on them. If you happen to have an old tea strainer that you plan never to use for tea again or an old mesh colander, you can use that to strain the beads out when you pour the sample into a smaller container. The other option is a small open-nosed syringe–the kind you use to give liquid medications–to get the sample from the box to container.
My other cat, who wasn’t as sensitive, was happy to pee on a clean plastic liner in the litter box with no beads.
Does she by any chance pee on the sidewall of the box? I had a cat that needed to give such a sample who did this often, I taped a few plastic ziplock bags (they are all I had) around the sides of the litter box and in a few hours a perfect sample was neatly deposited in a single bag.
Unless you’re worried your cat’s pissing acetone, I don’t think that’s a risk.
Assuming you mean “styrofoam packing peanuts” literally. Starch-foam packing material would dissolve into starch goo, which would qualify as contamination. 